Emergency officials extended evacuation orders to two more towns threatened by a deadly array of wildfires in north-central Washington state as dozens of blazes swirled across the drought-parched Pacific Northwest and surrounding regions.

President Barack Obama signed a federal declaration of emergency for Washington state on Friday, authorizing the U.S. Department of Homeland Security and the Federal Emergency Management Agency to coordinate relief efforts in 11 counties and several Indian reservations hard hit by wildfires.

Authorities late on Thursday ordered the population of Tonasket, a riverfront hamlet of about 1,000 residents just 25 miles south of the Canadian border, to flee their homes as flames closed in.

About 25 miles farther south along the same river, emergency officials early on Friday issued additional evacuation orders for parts of Okanogan, a larger town at the western edge of the Colville Indian Reservation, urging evacuees in a Facebook posting "not to wait for door-to-door notification."

Both communities were in the path of flames from an array of wildfires dubbed the Okanogan Complex, which has doubled in size since Thursday to scorch some 161,000 acres of brush and dry timber about 115 miles (185 km) northeast of Seattle.

The Okanogan Complex includes the so-called Twisp River fire, which killed three firefighters on Wednesday night after forcing the evacuation of some 4,000 households in the towns of Twisp and Winthrop about 30 miles west of Okanogan in the foothills of the Cascades.

At least 70 large wildfires or clusters of fires have raged this week through several bone-dry Western states, the bulk of them in Washington, Oregon, Idaho, California and Montana, the National Interagency Fire Center in Boise reported.

The blazes, under attack by more than 30,000 firefighters and support personnel, have collectively charred more than 1 million acres of land across the region.

Fire-suppression costs in the Pacific Northwest alone are estimated to have exceeded $115 million to date, according to the fire center.

With manpower and other resources stretched thin, fire managers have turned to the U.S. military and even personnel from Canada, Australia and New Zealand to furnish reinforcements.

So far this year, U.S. wildland blazes have claimed the lives of at least 13 firefighters, four more than died in the line of duty during all of 2014, the fire center said.

Earlier this week, the governors of Oregon and Idaho joined Washington state in calling up state National Guard troops backed by military aircraft to help combat blazes.